Synthesis of many retroviral protease and renin inhibitors containing a hydroxyethylamine, hydroxyethylurea or hydroxyethylsulfonamide isostere include the preparation of a key chiral amine intermediate. The synthesis of the key chiral amine requires a multi-step synthesis starting from a chiral amino acid such as L-phenylalanine. The key chiral amine intermediate can be prepared by diastereoselective reduction of an intermediate amino chloromethylketone or amine opening of a chiral epoxide intermediate. The present invention relates to a cost effective method of obtaining enantiomerically, diastereomerically and chemically pure chiral amine intermediate. This method is applicable for large scale (multikilogram) productions.
Roberts et al. (Science, 248, 358 (1990)), Krohn et al. (J. Med. Chem. 344, 3340 (1991)) and Getman et al. (J. Med. Chem., 346, 288 (1993)) disclosed the synthesis of protease inhibitors containing the hydroxyethylamine or hydroxyethylurea isostere which include the opening of an epoxide generated in a multi-step synthesis starting from an amino acid. These methods also contain steps which include diazomethane and the reduction of an amino chloromethyl ketone intermediate to an amino alcohol prior to formation of the epoxide. The overall yield of these syntheses are low and the use of explosive diazomethane additionally prevents such methods from being commercially acceptable.
Tinker et al. (U.S. Pat. No. 4,268,688) disclosed a catalytic process for the asymmetric hydroformylation to prepare optically active aldehydes from unsaturated olefins. Similarly, Reetz et al. (U.S. Pat. No. 4,990,669) disclosed the formation of optically active alpha amino aldehydes through the reduction of alpha amino carboxylic acids or their esters with lithium aluminum hydride followed by oxidation of the resulting protected beta amino alcohol by dimethyl sulfoxide/oxalyl chloride or chromium trioxide/pyridine. Alternatively, protected alpha amino carboxylic acids or esters thereof can be reduced with diisobutylaluminum hydride to form the protected amino aldehydes.
Reetz et al. (Tet. Lett., 30, 5425 (1989) disclosed the use of sulfonium and arsonium ylides and their reactions of protected .alpha.-amino aldehydes to form aminoalkyl epoxides. This method suffers from the use of highly toxic arsonium compounds or the use of combination of sodium hydride and dimethyl sulfoxide which is extremely hazardous in large scale. Sodium hydride and DMSO are incompatible (Sax, N. I., "Dangerous Properties of Industrial Materials", 6th Ed., Van Nostrand Reinhold Co., 1984, p. 433). Violent explosions have been reported on the reaction of sodium hydride and excess DMSO ("Handbook of Reactive Chemical Hazards", 3rd Ed., Butterworths, 1985, p. 295).
Matteson et al. (Synlett., 1991, 631) reported the addition of chloromethyllithium or bromomethyllithium to racemic aldehydes. J. Ng et al. (WO 93/23388 and PCT/US94/12201, both incorporated herein by reference in their entirety) disclose methods of preparing chiral epoxide, chiral cyanohydrin, chiral amine and other chiral intermediates useful in the preparation of retroviral protease inhibitors.
Various enzyme inhibitors, such as renin inhibitors and HIV protease inhibitors, have been prepared using the above described methods or variations thereof. EP 468641, EP 223437, EP 389898 and U.S. Pat. No. 4,599,198 for example describe the preparation of hydroxyethylamine isostere containing renin inhibitors. U.S. Pat. No. 5,157,041, WO 94/04492 and WO 92/08701 (each of which is incorporated herein by reference in its entirety) for example describe the preparation of hydroxyethylamine, hydroxyethylurea or hydroxyethylsulfonamide isostere containing retroviral protease inhibitors.